The present invention relates to a suction throttle valve of a variable displacement compressor for use, for example, in an automotive air conditioning system and, more particularly, to a suction throttle valve of a variable displacement compressor for reducing the vibration and noise development that are due to pulsation of the suction refrigerant gas.
There is generally known a variable displacement compressor which is designed for use in an automotive air conditioning system and the like and capable of variably controlling its displacement. Such variable displacement compressor will be referred to merely as a “compressor” hereinafter. The compressor often generates noise which is due to pulsation of the suction refrigerant gas produced when the compressor is operating with a low flow rate of the suction refrigerant gas. For reducing the development of such noise, some compressors use a suction throttle valve which is provided in the suction passage between the inlet and the suction chamber for changing the opening area of the suction passage in accordance with the flow rate of the suction refrigerant gas.
Japanese Patent Application Publication No. 2000-136776 discloses a compressor having this type of suction throttle valve. In the compressor of this reference, a gas passage is formed between the inlet and the suction chamber, and a valve working chamber is formed between the gas passage and the inlet. An opening control valve is vertically movably arranged in the valve working chamber. The opening control valve is urged upward by a spring accommodated in a valve chamber which is formed in the valve working chamber. The opening control valve is moved upward or downward thereby to control the opening area of the gas passage in accordance with flow rate of the suction refrigerant gas drawn into the suction chamber through the inlet. The valve chamber communicates with the suction chamber through a communication passage. The opening control valve has a hole formed therethrough.
When the flow rate of the suction refrigerant gas is high, the pressure difference between the inlet and the suction chamber is increased. Thus, the opening control valve of the compressor according to the above reference is adapted to move downward against the urging force of the spring, thereby enlarging the opening area of the gas passage. Meanwhile, when the flow rate of the suction refrigerant gas is low, the pressure difference between the inlet and the suction chamber becomes small. Thus, the opening control valve of the compressor is adapted to move upward by the urging force of the spring, thereby reducing the opening area of the gas passage. This throttling effect of the opening control valve helps to reduce the noise caused by the pulsation of the suction refrigerant gas when the flow rate of the suction refrigerant gas is low.
The valve chamber accommodating therein the spring has a damping mechanism which is operable to urge the opening control valve upward. The damper effect acting on the opening control valve varies in accordance with the gas-tightness of the valve chamber. That is, the damper effect is enhanced with an increase of the gas-tightness of the valve chamber, but reduced with a decrease of the gas-tightness. The valve chamber communicates with the suction chamber through the communication passage which has a substantially constant diameter and communicates with the inlet through the hole formed in the opening control valve. Thus, the gas-tightness of the valve chamber is not sufficiently high and, therefore, the damper effect acting on the opening control valve is not sufficiently high, with the result that the damper effect is constant regardless of the flow rate of the suction refrigerant gas.
The damper effect prevents the opening control valve from moving when the compressor is operating with a high flow rate of the suction refrigerant gas, so that sufficient opening area of the suction passage may not be accomplished. The damper effect against the pulsation of the suction refrigerant gas may not be obtained sufficiently during compressor operation with a low flow rate of the suction refrigerant gas. Therefore, the spring constant needs to be set relatively large for increasing the throttle effect during compressor operation with a low flow rate of the suction refrigerant gas. However, if the spring constant is set too large, the required opening area is not obtained because the suction passage is throttled too much during operation with a high flow rate of the suction refrigerant gas. Thus, the compressor of the above-cited Publication is unable to fulfill simultaneously the above requirements. That is, there are requirements which are to enhance the effect of throttling the suction passage during compressor operation with a low flow rate of the suction refrigerant gas and to ensure sufficient opening area of the suction passage during operation with a high flow rate of the suction refrigerant gas. Therefore, the opening control valve of the above compressor is not movable smoothly in response to the variation of the flow rate of the suction refrigerant gas. Consequently, it is difficult for the opening control valve to maintain the performance of the compressor according to the variable operating condition of the compressor.